The present invention relates to a device for the controlled treatment of food liquids by means of steam. In particular, the invention relates to the heating and/or frothing up of food liquids, in particular milk, milk-containing drinks and similar liquids, such as soya milk, by means of steam.
Milk is usually foamed by means of steam or via mechanical means, such as e.g. coiled stirrers. In the hotel, restaurant and catering trade, steam is the method used most often. A steam generator produces steam, which is blown into a jug filled with milk via a steam pipe. Producing foamed milk of the correct texture, temperature and consistency requires extensive experience and expertise of the barista.
Devices are known attempting to partly emulate the knowledge and expertise of the barista. It is known from e.g. EP 2633788, to incorporate a temperature probe in the steam pipe. A control unit, connected to the temperature probe, controls the supply of steam on the basis of the desired type of foam and stops the supply when the desired final temperature is reached. Since the temperature probe protrudes from the steam pipe, such a device is more difficult to clean.
EP 2229850 describes a device in which the steam pipe is arranged so as to be moveable. The device may be provided with a programme containing a movement path for the steam pipe which depends of the desired milk foam. A temperature sensor may be provided in order to select an optimum movement programme for the steam pipe on the basis of the temperature of the milk to be foamed. EP 2229850 provides a float on the steam pipe in order to ensure a constant distance between the end of the steam pipe and the liquid level. Such a float not only results in a complicated construction, because the steam pipe has to be arranged in a sprung manner. The float also forms an obstacle when cleaning the appliance. On the other hand, EP 2229850 provides an active movement element for actuating a movement of the steam pipe which element is connected to a sensor for detecting the liquid level, in which the movement of the steam pipe is actuated depending on the measured values of this sensor.
In order to obtain milk foam of good quality using the abovementioned devices, it is important to correctly determine the liquid level. However, air bubbles or other contaminants are often present on the liquid surface of milk and prevent accurate measurement, as a result of which an appliance cannot function properly and cannot deliver foam of consistent quality.